Use of both non-polar solvents, like butane and propane, and polar solvents, like ethanol, to extract active cannabinoids and terpenes from raw cannabis plant material is well known to practitioners of the art of cannabis oil extraction. Extraction solvents also separate out undesirable non-polar byproducts such as waxes, fats, and lipids from the plant material during extraction. These byproducts must be removed from the product stream, which is typically done with a cooling process to coagulate the waxes to make them amenable to straightforward filtering techniques. This filtering can be done in-line with a closed-loop process with solvent entering an extraction column on one end and exiting and passing through the filter stack at the other, through refrigerated post-processing of the extracted mixture, or a combination of these techniques.
Cooling is also used for “Live Resin” extraction, which requires sustained cold temperatures because the plant material must remain frozen since it is fresh rather than dried and cured. The water content inside the plant material is frozen for the duration of the extraction, otherwise the water (which is a polar solvent) will ruin the extract by pulling out unwanted plant constituents, such as green chlorophyll.
Current state of the art is limited to minimum coagulation temperatures bounded by the practical range of readily available, cost-effective cooling options such as “dry ice” (frozen CO2) or recirculating chillers using glycol or water-glycol mixtures. With consideration for equipment cost, logistics, electric power, etc., −30° F. to 10° F. has proven to be a typical operating range.